This invention is related to spinning packs for the production of synthetic fibers from polymer melts. More particularly, the invention is an improved filter to be used in the spinning pack.
A conventional spinning pack assembly for the extrusion of synthetic fibers includes a large central cavity containing filter media through which molten plastic material is forced at extrusion pressures. A spinneret disc is attached to the spinning pack assembly and contains small orifices for extrusion of individual fiber strands. Various filter media are placed in the cavity above the spinneret disc to shear the polymer and to filter out foreign particles which might clog the spinneret orifices. The filter media may be of loose material, for example, metal filings or sand, or may be a sintered metal disc.
In studies of polymer flow through various kinds of filtration media, it has been discovered that the surface area available for filtration is one of the most critical variables in the process. The greater the filtration surface area, the higher the capacity of the filter to collect impurities. A desirable method of increasing the effective filtration area is to use sintered porous filters made in a variety of geometric shapes.
U.S. Pat. No. 3,729,279 shows a configuration of upstanding concentric rings containing outflow bores. While these filters are an improvement by providing a greater surface area for filtration than the previous particulate material normally used, they still are not completely satisfactory because as the number of concentric grooves increases the wall thickness between each groove necessarily decreases thus weakening the filter making it susceptible to collapse when operating at high pressure.